A reversible-flow pre-run check for lattice-Boltzmann mixing: the collision operator controls scalar fidelity

Companion data and code. A compact tracer blob is stirred for a time T, the driving is reversed and advanced a further T, and the recovered field is scored against the initial blob by a normalized reconstruction fidelity R. The archive contains the OpenLB 1.9 (CUDA) and FluidX3D (OpenCL) advection–diffusion setups for three flows (analytic Taylor–Green vortex, lid-driven cavity, Taylor–Couette), the parameter-sweep output backing every figure (anti-smear R(Pe), the reversible-to-irreversible R(Re) transition, the BGK-vs-TRT collision-operator floor, and the cross-code overlay), and the figure-generation scripts. Reported R are single-run point estimates; read trends (monotonicity, sign, scheme ordering), not uncertainty-quantified magnitudes.